There is a recent article in the Archives of Environmental Contamination and Toxicology that is getting quite a bit of press. This article suggests that a common ingredient in sunscreen is extremely toxic to corals and could be part of the cause of coral bleaching. One phenomena that has been somewhat puzzling is why bleaching is more severe in area with heavy tourist traffic, and this might help explain that phenomena. Here's a link to the original article:

I tried to attach the PDF, but the file was too large, sorry. For more information, you can also do a Google search for "Oxybenzone", the ingredient that appears to be extremely toxic, even as low as parts per trillion.